Educational Resources-Brown Pelican/Biomagnifcation/DDT
Pelicanus occidentalis and information about Biomagnification and DDT
- Standard: I-1
- Standard: II-1
- Standard: III-3
- Standard: VI-1
“Pelicans almost disappeared from Texas because they were poisoned by the pesticide DDT, which caused them to lay thin-shelled eggs which broke during incubation. Because they were not able to produce young, the number of Pelicans dropped to less than 100 birds during the years 1967-1974. Since DDT was banned in 1972, Pelicans have made a steady comeback.” (TPWD)
- The American Brown Pelican is common along the coastlines of North and South America
- Their length is around 50″ long and have a 84″ wingspan
- They live in social groups and congregate in large flocks
- They nest in trees or on the ground in shallow bays
- Brown pelicans are primarily fish eaters. They have extremely sharp eyesight
- Once they locate a fish, they dive straight down into the water sometimes from 50-60 feet
- As they enter the water, they completely submerge and come up with a bill full of fish
- Other birds like terns, gulls and cormorants constantly hassle them and steal their food
Biomagnification and DDT
Three conditions must be present for Biomagnification to occur (Mader, 1996)
- The pollutant must be long-lived
- The pollutant must be concentrated by the producers
- The pollutant must be fat soluble
Producers will go to great lengths to obtain nutrients, sometimes even taking in more than they need and storing it. Chemical pollutants such as DDT resemble inorganic nutrients and are stored in the producer’s body, making the pollutant at a higher concentration in the producer than in the environment.
Consumers eat the producers, and since not much energy passes from one trophic level to the next the consumers consume large quantities of the producer and in turn large quantities of the pollutant and moves in to the fat storage of the consumers.
The best example is DDT; a long lived pesticide (half life of 15 years) developed to improve human health by killing mosquitoes. It was extremely effective because it did not break down in the environment, but it causes some severe long term effects on birds. DDT interfered with the deposit of calcium into the egg shells. As the eggs were laid their shells were extremely soft and would often break and the number of birds started to decline. The brown pelican and Bald eagle have made comebacks due to the ban of DDT pesticide.